# Rollercoaster Fun

1. Nov 6, 2005

Riding a Loop-the-loop. A car in an amusement park ride rolls without friction around the track shown in the figure. It starts from rest at point A at a height h above the bottom of the loop. Treat the car as a particle.

What is the minimum value of h (in terms of R) such that the car moves around the loop without falling off at the top (point B)?

I have no clue what to do.

Last edited by a moderator: Apr 21, 2017
2. Nov 6, 2005

### lightgrav

why WOULD it fall off at point B?

What's the shape of the path you WANT it to travel on?

Did you draw a Free-Body-Diagram of the coaster at B?

3. Nov 6, 2005

i posted a picture. Thats the link.

4. Nov 7, 2005

### lightgrav

What I asked was, did YOU draw the Forces that act on the coaster,
and label them according to what caused them?
Why do we do that all the time?

5. Nov 7, 2005

YES. I DREW A FREE BODY DIAGRAM. It would fall off if the weight did not equal the centripital force.

6. Nov 7, 2005

### lightgrav

so set the weight equal to m v^2/r, and solve for v needed at top.

Now, how to get that speed there ...
have you done PE and KE , yet? that's the best approach here.

7. Nov 7, 2005

we just started pe, and ke

8. Nov 7, 2005

### lightgrav

perfect.
The PE_gravitational at the start (height H) + Work done by friction (=0)
becomes PE_grav + KE at point B.

What's the height at B? What KE did you need there?

Last edited: Nov 7, 2005